1. Field of the Invention
The present invention generally relates to protection systems for computer hard disk drives in portable computers and, more particularly, to, a reflexive system for parking the heads of a hard disk and, optionally, stopping the spinning of the magnetic media platters in the event the computer is dropped.
2. Description of the Prior Art
Portable personal computers (PCs) have become more and more popular. Part of this popularity is due to providing portable computer with much the same power and features of desk top workstations. Among these features are hard disks which are now quite common in portable computers.
Portable computers are subject to forms of failure which are not a problem for desk top workstations. They can run out of power and they can be dropped. While this latter jeopardy is a threat to every component in the system, it is the hard disk drive which has the lowest threshold of failure in the event the computer is dropped. This component is so vulnerable to shock because it is dependent on the maintenance of a very small gap between the drive heads and the disk platters. The size of this gap is a key factor in the quantity of data which can be stored on the disk. In general, the smaller the gap, the more the data which can be stored. Thus, small, and hence vulnerable, gap dimensions are the rule for hard disks. The technology routinely used to obtain small gap height is aerodynamic. The head is literally flown over the platter surface to place the heads as close to the platters as possible without allowing contact. If the head were to contact the platter, the result could be both the destruction of the head and the removal of magnetic material (and hence data) from the platter.
Disk manufacturers recognize this hazard and attempt to address it by shock mounting their drives, by publishing the G-force limits their drives can tolerate, and by providing a position in which the heads may be "parked" in which the drive can tolerate accelerations which are far greater than are tolerable when the heads are "loaded".
The prior art addresses two kinds of events which may destroy the data integrity or hardware integrity of a hard disk. One of these event types is electrical power failure. This problem is addressed, for example, in U.S. Pat. No. 4,786,995 to Stupeck et al., U.S. Pat. No. 4,831,469 to Hanson et al., and U.S. Pat. No. 4,866,554 to Stupeck et al. In each of these patents, the energy stored in the motion of the disk heads is tapped by using the disk spindle motor as a generator. The power derived from this source is used to retract the disk head. Electromagnetic braking of the spindle is also contemplated. Provisions are made by one invention to shut down in the event of other voltage faults beside that of power failure.
The second event type is physical or mechanical impact. In U.S. Pat. No. 4,040,103 to White, an accelerometer is used to detect the magnitude and direction of a shock so that the hard disk head flying height can be adjusted. This adjustment is possible because the accelerometer is mounted on the disk driver frame while the drive itself is mounted to that frame by shock absorbers. The time delay for shock transmission supplied by the shock absorbers allows the flying height correction to be calculated prior to the shock arriving at the disk head.
In U.S. Pat. No. 4,862,298 to Genheimer et al., impact detection is used to generate a write-fault signal to the computing system. This signal is used to prevent data destruction by off-track writes and to cause head retraction in the event of severe impacts. This device relies on the fact that the read and write operations on disk drives involve sectors of significant extent so that if an impact is detected, it is very likely that it will occur in the course of a sector operation rather than at its very end. The system is thus expected to have the time required to abort the read or write operation without storing or retrieving corrupted data.
The problems with each of these techniques is that remedial action is taken after the failure or impact has occurred and may be too late to prevent damage. In the case of impact, what is needed is a system which can anticipate the possibility of impact and take protective action before the impact actually occurs.